It is known to connect a shaft to another shaft or to a hub of a wheel or pulley by means of a fluid-pressure actuated coupling that merely creates a pressure or interference fit between the two parts being joined. Such an arrangement, as described in U.S. Pat. No. 3,865,497 to A. E. Bratt et al., has a frustoconically tapered surface on the shaft or on a collar used to join two shafts. A complementarily shaped bore of a sleeve can be fitted over this surface. One end of the sleeve is formed at the narrow end of the frustoconical surface with an axially outwardly and radially inwardly open groove. A ring threaded on the shaft or collar and a seal washer axially close off this groove, which is radially inwardly closed by the shaft or collar to form a closed annular chamber that can be vented through a normally sealed bleed opening. The sleeve is formed at the frustoconical surface engaging the shaft with a radially inwardly open groove to which hydraulic fluid is fed under high pressure, so that it will seep axially along between the frustoconical surface and the sleeve and will eventually pressurize the annular chamber, thereby urging the sleeve toward the bigger end of the frustoconical surface to tighten the coupling. To release the coupling the vent hole is opened so the flow of oil between the sleeve and frustoconical surface reduces the friction between them sufficiently to slide the sleeve back toward the smaller end of the frustoconical surface. This system is a variation on the systems described in U.S. Pat. Nos. 3,228,102 of R. E. Sillett and 3,531,146 of N. A. Blad and A. E. Bratt.
In this arrangement when the collar is used to join two shafts it is impossible to obtain the same clamping pressure on both shaft ends. The thicker part of the collar will not be radially inwardly deformed as the thinner part so that the shaft end gripped thereby will be less forcibly held. After having been in use a long time it is frequently very difficult to open up the coupling, particularly when, as is common, the various parts have bitten mechanically into one another. Thus it is standard practice to open up such a coupling after a long time in use by means of a hydraulic gear puller. The coupling must, in addition, be machined extremely precisely for an exact surface-contact fit between the frustoconical surfaces. Such production makes the coupling quite exensive.